The typical lance drive comprises a rigid lance mount to which the lance connects. The lance mount may take a variety of forms, but must allow for used lances to be removed from the lance drive and for new lances to be mounted on the drive. In a known lance mount configuration, a swing-gate design is used to clamp the lance into the lance mount of the lance drive. This swing-gate consists of a thick steel bar sandwiched between two other steel bars. A pivot pin will be run through all three bars and will allow the middle bar to swing open like a gate. Once the lance is mounted to the lance and the gate is closed, a threaded rod with wing nut will anchor it firmly on the lance drive. Typically, the top of the lance will include a structural steel member, which can be round or square, to which the lance can be attached to the lance drive.
At the top of the lance is a connection to which reagent or gas transport piping or hose will connect. This connection could be threaded, flanged, or attached using other means. To allow movement of the lance, the top connection will typically be made with flexible hose. Once the lance is connected to the transport pipe or transport hose and the lance is firmly in the lance mount on the lance drive, the lance can be driven by the lance drive into the molten bath for treatment of iron or steel. Other than a vertical movement into the molten metal, the typical lance drive provides has no other range of motion to the lance. This “fixed” lance drive may be used with a bottom blow lance, a Tee lance, or a dual port lance.
To improve efficiency and reduce process time, rotary lance drives were developed that rotate the lance in addition to providing vertical movement. Rotary lance drives are described in U.S. Pat. No. 4,426,068 (Gimond et al.) and U.S. Pat. No. 7,563,405 (De Castro). Rotary motion distributes the powdered reagents to a larger reaction zone in the bath compared to fixed lance treatment. Known rotary lance systems use a Tee lance having two outlets, and the lance is rotated continuously through 360 degree circles.
Existing rotary lance drives, including a lance drive made by applicant, include a swivel connection at the top of the lance drive to allow for rotation of the lance without twisting the reagent supply hose feeding into the transport pipe or transport hose of the lance drive. In applicant's existing rotary lance drive design, shown in FIGS. 1-4, a swivel connection 2 is connected to a reagent transport pipe 4 which extends through the rotary lance drive mechanism to a connection 6 at the top of the lance 8. To rotate the lance, the existing rotary lance drive uses a motor 10 which rotates a hollow drive shaft 12 connected to the motor by a gear drive 14. The hollow shaft 12 is necessary to allow passage of the reagent transport pipe 4 from the swivel connection 2 to the connection 6 at the top of the lance 8. The hollow drive shaft 12 is supported by two rotary bearings 16 which are spaced sufficiently to take the radial and axial loads. The gear drive 14 is connected to an upper portion of the hollow drive shaft 12. A lower end of the hollow drive shaft 12 is rigidly connected to a lance mount 18 that clamps the lance 8 in place. In the existing rotary lance drive, the two rotary support bearings 16 are internal and require the entire drive mechanism to be disassembled for periodic maintenance or replacement. Another drawback is that the reagent transport pipe 4 has two connections (swivel connection 2 and lance connection 6) that are a source of leaks and require maintenance.
Regarding injection lances carried by lance drives, the most common lance design is the bottom-blow lance. In its center is a steel pipe through which gas and powdered reagents are transported into molten iron or molten steel. Typically, the top will include a structural steel member, which can be round or square, by which the lance can be attached to the lance drive. To protect the transport pipe from the molten metal, a lower portion of the lance will coated with a refractory material which insulates the pipe from the intense heat. The refractory portion has a circular cross-sectional shape. A variation of the basic bottom-blow lance is the Tee lance, which is less common than the bottom-blow lance but nevertheless is currently being used. The Tee lance has two separate discharge ports facing discharge directions which are 180 opposite one another. The two ports discharge ports are fed by a single main pipe conduit with a Tee at the bottom. As with the bottom-blow lance, the Tee lance includes a steel pipe defining the main conduit, a structural steel top, and a refractory bottom. The benefit of this design is that the powdered reagent is split into two zones instead of one. The standard Tee lance is currently the preferred design for rotary lance drives.
A dual port lance is known from U.S. Pat. No. 5,188,661. The dual port lance includes two independent pipes through which two streams of powder reagent or gas can pass. This allows twice as much material to feed into the molten bath, thereby reducing the time needed to treat the metal. This offers a great advantage in minimizing treatment time which allows for more production by a steel mill.